1. Field of the Invention
The present invention is related to a power device capable of improving flicker of a liquid crystal display, a liquid crystal display capable of improving flicker, and method thereof, and particularly to a power device capable of improving flicker of a liquid crystal display, a liquid crystal display capable of improving flicker, and method thereof that utilize an alternating current low gate voltage to improve flicker caused by an alternating current common voltage.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a diagram illustrating a plurality of pixels included by a thin film transistor liquid crystal display (TFT-LCD) according to the prior art. As shown in FIG. 1, each pixel includes a thin film transistor 102, a liquid crystal capacitor CLC, and a storage capacitor CS, where a gate G of the thin film transistor 102 is coupled to a gate line G1, a source S of the thin film transistor 102 is coupled to a data line D1, and a drain D of the thin film transistor 102 is coupled to a liquid crystal capacitor CLC and a storage capacitor CS. In addition, another terminal of the liquid crystal capacitor CLC and another terminal of the storage capacitor CS are coupled to a common electrode COM.
Please refer to FIG. 2 and FIG. 3. FIG. 2 is a diagram illustrating a pixel 200 of the thin film transistor liquid crystal display, and FIG. 3 is a diagram illustrating relationships of a voltage stored in a storage capacitor CS and a liquid crystal capacitor CLC, a data voltage VDATA of the data line D1, a common voltage VCOM, a high gate voltage VGH and a low gate voltage VGL of the gate line G1. As shown in FIG. 2, the pixel 200 includes a thin film transistor 202, a liquid crystal capacitor CLC, and a storage capacitor CS, where a parasitic capacitor Cgd exists between a gate G and a drain D of the thin film transistor 202. As shown in FIG. 3, when the thin film transistor liquid crystal display displays an Nth frame, the thin film transistor 202 is turned on according to the high gate voltage VGH of the gate line G1, so the data voltage VDATA of the data line D1 charges the liquid crystal capacitor CLC and the storage capacitor CS. Meanwhile, a voltage of the drain D of the thin film transistor 202 is gradually increased to a voltage VP1. When the thin film transistor 202 is turned off according to the low gate voltage VGL of the gate line G1, the voltage of the drain D of the thin film transistor 202 instantly reduces a feedthrough voltage ΔVP due to a capacitive effect of the parasitic capacitor Cgd. That is to say, the voltage the drain D of the thin film transistor 202 is decreased to a voltage VP2. Similarly, when the thin film transistor liquid crystal display displays an (N+1)th frame, the voltage of the drain D of the thin film transistor 202 also reduces the feedthrough voltage ΔVP. Thus, the thin film transistor liquid crystal display has flicker because a positive feedthrough voltage ΔVPP is unequal to a negative feedthrough voltage ΔVPN. In addition, the feedthrough voltage ΔVP is determined by conservation of charge and equation (1):
                              Δ          ⁢                                          ⁢          VP                =                              Cgd                          Cgd              +              CLC              +              CS                                ⁢          Δ          ⁢                                          ⁢          VG                                    (        1        )            
As shown in equation (1), ΔVP=VP1−VP2, and AVG=VGH−VGL.
As shown in FIG. 3 and equation (1), when the common voltage VCOM provided by the common electrode COM is a direct current voltage, a thin film transistor liquid crystal display designer can compensate the flicker of the thin film transistor liquid crystal display caused by the feedthrough Voltage ΔVP by adjusting a direct current level of the common voltage VCOM. Meanwhile, the common voltage VCOM is determined by equation (2):
                              Δ          ⁢                                          ⁢          VCOM                =                                            Δ              ⁢                                                          ⁢              VDATA                        2                    -                      Δ            ⁢                                                  ⁢            VP                                              (        2        )            
As shown in FIG. 3, ΔVDATA is a difference between a high voltage and a low voltage of the data line D1. Please refer to FIG. 4. FIG. 4 is a diagram illustrating relationships of a voltage stored in the liquid crystal capacitor CLC and the storage capacitor CS, the data voltage VDATA of the data line D1, an alternating current common voltage VCOMAC (a high common voltage level VCOMH and a low common voltage level VCOML), and the high gate voltage VGH and the low gate voltage VGL of the gate line G1. In small and medium-sized thin film transistor liquid crystal display applications, the alternating current common voltage VCOMAC (the high common voltage level VCOMH and the low common voltage level VCOML) is usually used in the small and medium-sized thin film transistor liquid crystal displays due to low power and low cost requirements. As shown in FIG. 4, when the thin film transistor 202 is turned off and the alternating current common voltage VCOMAC is the low common voltage level VCOML, a low feedthrough voltage level ΔVPL is determined by equation (3):
                              Δ          ⁢                                          ⁢          VPL                =                              Cgd                          Cgd              +              CLC              +              CS                                ⁢          Δ          ⁢                                          ⁢          VG                                    (        3        )            
When the thin film transistor 202 is turned off and the alternating current common voltage VCOMAC is the high common voltage level VCOMH, a high feedthrough voltage level ΔVPH is determined by equation (4):
                              Δ          ⁢                                          ⁢          VPH                =                                            CLC              +              CS                                      Cgd              +              CLC              +              CS                                ⁢          Δ          ⁢                                          ⁢          VCOM                                    (        4        )            
In equation (4), ΔVCOM=VCOMH−VCOML. As shown in equation (3) and equation (4), because the high feedthrough voltage level ΔVPH is unequal to ΔVCOM, a voltage V1 is unequal to a voltage V2. Therefore, the thin film transistor liquid crystal display designer can not compensate the flicker of the thin film transistor liquid crystal display due to ΔVCOM being unequal to the high feedthrough voltage level ΔVPH by merely adjusting a voltage level of the alternating current common voltage VCOMAC.